1. Field of the Invention
This invention relates to an image processing apparatus, and more specifically to an image processing apparatus which can discriminate a characteristic of the image, such as characters versus halftone.
2. Related Background
A known image processing apparatus is structured in such a way that it performs image discrimination and copying with the same document scanning.
FIG. 12 is a schematic block diagram for explaining operation of the known image processing apparatus. As shown in FIG. 12, an image discrimination circuit 12-2 executes image discrimination, such as edge extracting, on image information input from a terminal (a). Circuit 12-2 generally must use a big area, for example, 10 pixels.times.10 pixels, for discriminating between a character region and a picture region precisely. In such case, the image signals are delayed for five (5) lines by the image discrimination circuit 12-2. Therefore, a delay circuit 12-1 is provided for delaying image signals input from terminal (a) for five lines in order to make an image processing circuit 12-3 process the image signals in program synchronism with the output of the discrimination circuit 12-2.
However, the above-described known image processing apparatus requires a large-scale delay circuit because image discrimination has to be executed prior to image processing. When the apparatus is a color copying apparatus, the image signals comprise red, green, and blue multi-level image signals. This has resulted in the defect that an especially large-scale delay circuit is required to execute image discrimination on these three multi-level image signals.
A known color copier (or other image input/output apparatus) performs scanning of an original four times to make one copy from an original. For example, the apparatus outputs a yellow component signal (Y) based on each of the blue component signal (B), the green component signal (G), and the red component signal (R), which are obtained by means of the first original scanning, and reproduces a yellow toner image. The apparatus also outputs a magenta component signal (M), a cyan component signal (C), and a black component signal (BK), each based on each of the color component signals (B), (G) and (R), which are all read again during each second, third, and fourth original scannings, and reproduces magenta, cyan, and black toner images, respectively. These four toner images are superposed to form a full color image.
It is preferable to reproduce an edge portion of a black character with only black toner because doing so makes the reproduced image of the black character stand out. However, it is impossible to read precisely the same point on an original repeatedly in each of four consecutive original readings because of mechanical wear or vibrations. For example, in the case where approximately the same point on the original, from which only the blue component signal (B) is output at the first original scanning, is read four times, the blue, green, red component signals may be output with the same rate. This has resulted in the defect that what should be the reproduction of a black edge portion of the original is not only not completely black but also is blurred.
Further, in the case where an original reading scanning system is driven by a stepping motor, the revolution speed of the stepping motor is lowered for an enlargement copying operation, as a result of which further color blurring occurs because of motor vibration. This has resulted in the defect that the quality of the reproduced image is vitiated, and the reproduced image is deficient in the reproduction of vivid colors.